Photosensitive lithographic printing master and process for preparation of a lithographic plate

ABSTRACT

A PHOTOSENSITIVE LITHOGRAPHIC PRINTING MASTER IS PREPARED FROM A SUPPORT SUCH AS A POLYETHYLENE TEREPHTHALATE FILM COATED WITH A HYDROPHILIC PHOTOSENSITIVE SILVER HALIDE EMULSION THE OUTER SURFACE OF SAID WMULSION BEING OLEPHILIC AND WATER-PERMEABLE. THE SURFACE OF THE SUPPORT IN CONTACT WITH THE EMULSION CAN BE COATED WITH A HYDROPHILIC LAYER SUCH AS A GELATIN LAYER CONTAINING SILICA PARTICLES.

United States Patent O 3,561,961 PHOTOSENSII lVL LITHOGRAPHTC PRINTINGMASTER AND PROCESS FOR PREPARATHON OF A LITHOGRAPHIC PLATE RalphKingsiey Blake, Westfield, Ni, assignor to E. I. du Pont de Near-oursand Company, Wilmington, Del., a corporation of Delaware No Drawing.Filed Feb. 20, 1967, Ser. No. 617,078 Int. Cl. Gillie 1/78, 5/00; G03f7/02 US. Cl. 96-33 17 Claims ABSTRACT OF THE DISCLOSURE DESCRIPTION OFTHE PRIOR ART Various photographic methods are employed in thelithographic industry for the formation of a positive oleophilic imageon a hydrophilic surface of a lithographic printing plate from a highcontrast line or halftone original. Within the meaning of thisinvention, oleophilic means a surface which accepts greasy ink andhydrophilic means a surface which accepts water. A positive oleophilicimage is one in which the oleophilic areas correspond to the black areasof the original and the areas corresponding to the clear areas of theoriginal are hydrophilic and oleophobic. A lithographic plate having apositive oleophilic image is defined as a positive-working plate. Apositive copy is a copy obtained from a positive working plate. A platehaving a negative oleophilic surface will produce a negative copy. Suchplates may be mounted on a roller of an oifset printing press and passedin contact with an aqueous fountain solution and a printing ink. Theinked image is applied to a rubber printing blanket and then transferredto the sheet to be printed. The method of producing plates oftenrequires complicated procedures as well as special films.

SUMMARY OF THE INVENTION The product of this invention in its broadestaspects comprises (a) a support such as a polyester film, (b) alight-sensitive hydrophilic gelatino-silver halide emulsion layer coatedon the support, and (c) an oleophilic waterpermeable surface on saidemulsion layer.

The support itself can have a hydrophilic surface. A support having ahydrophilic surface is defined as a (1) hydrophilic support which wouldnaturally have a hydrophilic surface, or (2) a support having ahydrophilic layer between the emulsion and the support.

This invention also encompasses the process of converting these novelfilm elements into a printing plate. The process comprises imagewiseexposing the novel element, developing the exposed silver image,treating said silver image with an etch-bleach bath which degrades thegelatin in the exposed areas, and in said areas, removing the oleophiliclayer covering the exposed silver image and the degraded emulsion layerthereby forming a hydrophilic surface in the etched areas. The resultantelement of this process produces an oleophilic/hydrophilic printingplate.

The oleophilic Water permeable surface on the emulsion can be obtainedin several ways. The following are methods, within the scope of thisinvention, of obtaining such oleophilic coatings:

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(a) Coating the emulsion surface with an oleophilic Werner-type chromiumcomplex having a hydrophobic group, e.g., complexes of myristic acid,stearic acid, etc.;

(h) Coating the emulsion surface with polyacrolein;

(c) Coating the emulsion surface with a mixture of and (d) Coating theemulsion surface with a solution of a polymeric dialdehyde;

(e) Coating the emulsion surface with elements of (a), (b), (c) or (d)mixed with a compatible binder such as gelatin;

f) Coating the emulsion surface with elements of (a), (b), (c), (d),either independently or mixed in any arrangement, and a surfactant suchas sodium dodecyl sulfate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The amount of oleophiliccoating will vary depending on the composition of the coating.Consequently, a simple empirical determination with a particular coatingwill give the desired coating for any given element. The oleophilicsurface should be oleophilic enough to readily accept a conventionalquick-drying printing ink and yet the coating should still beWater-permeable. Too much of an oleophilic coating will preventprocessing of the exposed element with the standard aqueous developingsystems. When a hydrophilic layer is coated over the support, it ispreferably a gelatin coating containing colloidal SiO particles inamounts of 0 to 20 parts by weight, generally l to 12 parts by weight; ahardener usually a polymeric dialdehyde starch produced by the oxidationof of the anhydroglucose units of starch, in amounts of 0.4 to 10 partsby Weight, generally 1 to 4 parts by weight; and a surface wetting agentusually saponin and alcohol in amounts of 0.5 to 10 parts by weight,usually 1 to 3 parts by weight. The light-sensitive layer which coversthe SiO layer is preferably a gelatino-silver halide emulsion containingsilver bromide, silver chloride or mixtures thereof, usually containingat least 50 mole percent silver chloride. The polymeric dialdehyde mayalso be present in the emulsion in the same limits of about 0.4 to 10parts by weight. The oleophilic overcoating for this particular elementis preferably comprised of a Werner chromium complex of stearic ormyristic acid in amounts of 30 to 70 parts by weight, a hardener such asformaldehyde in amounts of 0 to 40 parts by weight, usually 10 to 25parts by weight, and a surfactant, usually sodium dodecyl sulfate, inamounts of 5 to 40 parts by weight and preferably 10 to 33 parts byweight. All parts by weight in this particular preferred element are thefinal dry, photosensitive product.

When using an element containing the hydrophilic support surface, thephotosensitive element is fully exposed to actinic radiation to form alatent image throughout the thickness of the silver halide emulsion. Theimage is completely developed in a conventional high contrastlithographic developer such as hydroquinone and sodium bisulfite. Afterdevelopment, the photosensitive element is bathed in an acid peroxide,etch-bleach solution containing a halide in amounts of 0.1 g./l. to 1'0g./l., a conventional bleaching salt, e.g., cupric nitrate in amounts of0.5 g./l. to 70 g./l., an acid activator, e.g., lactic acid in amountsof 1 rnl./l. to rnl./l. and hydrogen peroxide in concentrations of 0.1%to 3.0%. The etch-bleach treatment oxidizes the developed silver imagecausing degradation of the binder in the presence of the developedsilver thus destroying the developed regions of the emulsion layer. Thesoftened binder in the exposed area may be removed by rubbing, down tothe hydrophilic surface of the support, or the support itself if thelatter is hydrophilic, leaving an oleophilic positive image surroundedby hydrophilic areas. This printing plate may then be mounted on aconventional offset printing press and using a fountain solution,preferably containing gum arabic and asphaltum and a conventionalquick-drying ink, many copies can be produced. It has been noted thatslightly improved printing plates were obtained from elements of thisinvention which were conditioned in an oven at about 120 F. and 65%relative humidity for several days before exposure and processing.

If a light-sensitive element is used as previously defined where saidelement has no hydrophilic support surface, the following modifiedprocess can be used to form the plates. This process comprises exposingand developing the photosensitive element, and then completely removingthe oleophilic overcoating in the exposed areas, and plurality removingthe developed silver image in the exposed areas. The removal of theexposed areas can be achieved by l) restricting the bleaching andetching of a fully developed silver image to the upper part of theemulsion layer by controlling the contact time, (2) restrictingdevelopment to limit the silver image to the upper part of the emulsionlayer followed by complete bleaching and etching of the developed imageby controlling the contact time, and (3) by limiting the exposure timeto restrict the image to the surface when developed. In the exposedareas, the oleophilic overcoating and the gelatin, degraded by theetching and bleaching, can be removed by rubbing, leaving an oleophilicpositive image surrounded by hydrophilic gelatin of the emulsion as thebackground area. The control over partial development or partial etchingis easily deter-mined empirically, depending on the thickness of thegelatinosilver halide layer. A variation of this invention is obtainedby overcoating the emulsion layer with the oleophilic overcoating afterexposure and development but before bleaching and etching.

A preferred photosensitive element for use in the process whichpartially removes the silver halide emulsion layer is prepared bycoating on a resin subbed polyethylene terephthalate film base, anorthochromatically, sensitized, lithographic, gelatino-silver halideemulsion generally containing at least 50 mol percent silver chloride,and an oleophilic surface overcoating coated from: (1) an ethanolsolution containing 0.1 g. to 1.0 g. of a Werner chrome complex ofstearic or myristic acid per 100 ml. of ethanol, or (2) a 75%25%ethanolwater solution, containing 0.05 g. to 0.5 g. of a sodiumbisulfite adduct of polyacrolein (average molecular weight:400,000) per100 ml. of solution. The weights of the Werner chrome complex are givenas a solution of 27% of the complex in isopropanol.

Since the polyacrolein coating has a tendency to harden when aged, it ispossible to use greater amounts of polyacrolein if the plate is usedwithin a short period of time after coating of the polyacrolein.

The preferred process of this aspect of the invention comprises exposingthe photosensitive element and then restricting the development of thenegative latent image to the surface of the emulsion. This can beaccomplished by using a developer which restricts development to thesurface of the emulsion. A preferred developer is a high pH developer,i.e., pH above 12.0 containing p-methylaminophenol sulfate in amounts of1 g. to 10 g. per liter of developer, sodium sulfite in amounts of 10 g.to 100 g. per liter, and sodium hydroxide in amounts of 1 g. to 50 g.per liter as well as other conventional developer additives. Theemulsion surface developed negative image is generally immersed in astop bath of 5% acetic acid and then placed in an acid-peroxide bathgenerally containing a halide in amounts of 0.1 g./l. to g./l., a heavymetal salt, e.g., cupric nitrate in amounts of 0.5 g./l. to 70 g./l., anacid activator, e.g., lactic acid (85%) in amounts of 1 ml./l. to 100ml./l., and hydrogen peroxide in concentrations of 0.1% to 3.0%. Duringthe bleaching and etching, usually 1 to 2 minutes, the silver image andgelatin in the exposed areas bleaches and becomes A polyethyleneterephthalate film base was prepared with a resin sub stratum asdisclosed in Example 4, Alles, US. Pat. 2,779,864. Over this subbed basethere was coated to a weight of 35 mg/dm. (AgBr equivalent) anorthochromatically sensitized emulsion containing mole percent AgCl, 20mole percent AgBr and 110 gm. of gelatin per mole of silver halide. Anantiabrasion layer of clear gelatin was then coated over the emulsionlayer. The following oleophilic water-permeable overcoating wasprepared:

Solution A p 1% aqueous sodium bisulfite adduct of polyacrolein,

(av. mol. wt. 400,000) 50 Water 25 Ethanol 25 Solution A was coated overthe antiabrasion layer at room temperature at 8 f.p.rn. and allowed toair dry.

The photosensitive element was then exposed through the base in contactwith a halftone positive image to a high intensity-tungsten filamentincandescent lamp, e.g., General Electric No. 2 Photofiood lamp, for 10seconds at a distance of two feet and operating at 20 volts.

The following developer solution was prepared:

Solution B Water800 m1. Na SO (anhydrous)80 g. p-Methylamino phenolsulfate1 g. Boric acid-5 .5 g. KBr-2 g. NaOH-24 g. Water to make 1000ml.

The exposed photosensitive element was developed for one minute inSolution B at 68 F. followed by short stopping for 15 seconds in a 5%acetic acid bath. Because of the high pH, 13.9, of Solution B and theuse of a developing agent whose oxidation product inhibits subsequentdevelopment, the developed image was restricted to the emulsion surface.

A bleach-etch solution was then prepared as follows:

Solution C Water200 ml. Cupric nitrate18.8 g. Potassium bromide1 g.Lactic acid )15.6 ml. Hydrogen peroxide (3 )250 ml. Water to make 1000ml.

The photosensitive element was bleached and etched in Solution C for 2minutes. In the exposed areas, the silver image was bleached and thegelatin binder degraded to such an extent that the degraded areas couldbe rubbed away to the hydrophilic surface of the gelatin binder of theemulsion, leaving a positive, oleophilic image in the unexposed areas.This prepared plate was then mounted on a conventional offset printingpress and using 5% acetic acid as the fountain solution and conventionalink, 1600 positive copies were obtained.

EXAMPLE 2 A film base was prepared as in Example 1 and then coated withthe emulsion of Example 1, followed by an overcoating of a clear gelatinantiabrasion layer as in Example 1. An oleophilic overcoating was coatedfrom an alcohol solution, containing 1 gm. of the Werner chrome complexof myristic acid (27% of the complex in isopropanol) per 200 ml. ofethanol, at room temperature and 8 f.p.m. Exposure was the same as inExample 1 except that the photoflood lamp was operating at 30 volts.

After exposure, the film was developed in Solution B for one minutefollowed by short stopping in 5% acetic acid for seconds. Development ofthe photosensitive element in Solution B restricted the development ofthe latent image to the surface of the emulsion. The restricted imagewas then bleached and etched in Solution C for 2 /2 minutes. Thebleaching and etching caused the gelatin in the exposed areas to becomedegraded and softened. The softened exposed areas were then rubbed awaywith 5% acetic acid down to the hydrophilic gelatin binder found belowthe developed silver leaving a positive oleophilic image with a gelatinhydrophilic background suitable for printing copies thereof. Theprinting plate was then mounted on an offset printing press as inExample 1 and 22,600 positive copies were produced.

EXAMPLE 3 A film base of polyethylene terephthalate was prepared as inExample 1. A direct positive emulsion, as disclosed in assigneesapplication Ser. No. 392,625, filed Aug. 27, 1964, US. Pat. 3,361,564,Jan. 2, 1968, containing 15 mole percent silver chloride, 85 molepercent silver bromide, 0.0017 gram of morpholine borane per mole ofsilver halide and having a gelatin to silver ratio of 0.68 was coatedover the oleophilic film base. An oleophilic overcoating containing 10ml. of 1 percent polyacrolein resin as described in Example 1, 65 ml. ofwater, and ml. of ethanol was then coated over the hydrophilic directpositive emulsion at 8 ft./min. The photosensitive element was thengiven an image exposure using a General Electric No. 2 Photofiood at adistance of 24 inches for 20 seconds at 115 volts.

The following developer was prepared:

Solution D Component 1:

Water-500 ml.

Hydroquinone45 g.

Sodium sulfiteg.

Sulfuric acid, C.P. grade4 ml.

Water to make 1000 ml. Component 2:

Water500 ml.

Sodium carbonate-30 g.

Potassium carbonate90 g.

Potassium bromide8.3 g.

Sodium sulfite-90 g.

Water to make 1000 ml.

To make Solution D, equal parts of Component 1 and Component 2 wereused. Normally, ex osed elements are developed in Solution D for 45minutes, but the exposed element of this example was developed inSolution D for 2 minutes thereby restricting the development to thesurface of the emulsion. After development, the element was water washedfor /2 minute and then bleached and etched in Solution C for 2 minutes.Since the emulsion used in this example was a direct positive emulsion,the gelatin in the unexposed surface areas became degraded and wasremoved by rubbing. Etching in the unexposed areas was not completethereby leaving hydrophilic gelatin in the unexposed areas and anoleophilic image in the exposed areas. The element was rubbed with waterand a conventional black lithographic offset ink, the ink adhering onlyto the oleophilic exposed areas. The inked surface was then rolled incontact with a piece of white paper giving a direct negative inked imageon the paper. This process could be repeated to give many copies.

6 EXAMPLE 4 This is an example of total development and a partial bleachto produce a printing plate. A photosensitlve element including theWerner complex, oleophilic overcoating of Example 2 was prepared. Theelement was exposed as in Example 2. A developer was prepared asfollows:

Solution E Water800 ml. p-Methylaminophenol sulfate3 g. Sodium sulfite(anhydrous)50 g. Hydroquinone--9 g. Potassium carbonate-50 g. Potassiumbromide4.5 g. Water to make 1000 ml.

The exposed element was developed in Solution E for one minute and thenimmersed in a 5% acetic acid bath for 15 seconds. The developed elementwas bleached for 45 seconds in Solution C and immersed in the aceticacid solution for 15 seconds. The element was rubbed with a conventionallithographic ink. The ink held only to the unexposed, positive imageareas and not to the negative, exposed areas which were bleached andetched by Solution C to such an extent that the oleophilic surfacesoftened and rubbed away to leave some unoxidized negative silver imagebelow in the hydrophilic gelatin binder. This printing plate was testedas in Example 3 and many high quality copies produced.

EXAMPLE 5 A photosensitive element including the overcoated oleophilicpolyacrolein resin was pr pared as in Example 1. The element was exposedas in Example 1 and then r the silver image was surface developed forone minute in the following developer:

Solution F Solution F, of pH 13.4, was prepared by mixing 100 ml. of asolution containing 800 ml. of water, g. of Na SO 20 g. ofp-methylaminophenol sulfate, 5.5 g. of boric acid, 2 g. of KBr and waterto make 1 liter; ml. of a solution containing 800 ml. of water, 200 g.of Na SO 13.75 g. of boric acid, 5 g. of KBr, 60 g. of NaOH, and waterto make 1 liter; and 800 ml. of water.

Following development, the element was water washed for /2 minute andthen bleached and etched in the following solution:

Solution G Solution G is the same as Solution C of Example 1 except thatthe copper nitrate, potassium bromide, lactic acid, and hydrogenperoxide concentration were doubled prior to dilution to one liter.

The etching and bleaching treatment degraded the gelatin in the exposedareas to such an extent that the silver surface image could be rubbedaway leaving a positive, oleophilic image in the unexposed areassurrounded by hydrophilic gelatin of the emulsion in the exposed areas.The printing plate was then inked and successfully tested as in Example4.

EXAMPLE 6 This example describes a process of obtaining a negativeworking plate from the polyacrolein overcoated plate described inExample 1.

A photosensitive printing plate including the overcoating of sodiumbisulfite adduct of polyacrolein was prepared as in Example 1. Thephotosensitive element was exposed through its support to a negativetransparency as in Example. The exposed element was developed for oneminute in Solution E of Example 4 except that prior to dilution to 1liter with water, 2 grams of Na SO was added to Solution E. The originalexposed areas were developed to give a tough, tanned negative image. The

developed element was then water washed for A minute and bleached in thefollowing:

Solution H Potassium dichromate9.6 g. Sulfuric acid (conc.)10.7 ml.Water to make 1 1.

Following the bleaching in Solution H, the photosensitive element waswater washed for one minute and then subjected to white light. Followingexposure to white light, the image in the original unexposed areas wasdeveloped in Solution F of Example 5 for one minute, water washed for V:minute and then bleached and etched in the cupric nitrate, acid-peroxidebath, Solution C, Example 1 for 1% minutes. The second exposed imageetches much more rapidly than the first chrometreated negative image. Inthis manner the original unexposed areas can be rubbed away leaving anegative oleophilic image surrounded by hydrophilic gelatin. Thisnegative plate was inked and used to produce many high quality negativecopies.

EXAMPLE 7 Example 7 is an example of full developement in a conventionallithographic developer followed by a partial bleach and etch. After theelement of Example 5 was exposed as in Example 5, it was developed inSolution E of Example 4 for one minute. The developed element was waterwashed for one minute and then bleached and etched in the followingsolution for one minute.

Solution I M1. 3 M sodium chloride 100 1 M ferric nitrate 50 3 Mphosphoric acid 50 Water 300 3% hydrogen peroxide 500 Solution I is arapid acting, stable, surface bleaching and etching solution. Theexposed areas were degraded on the surface to such an extent that thesurface could be rubbed away leaving a positive, oleophilic imagesurrounded by hydrophilic gelatin in the exposed areas. The printingplate produced by the partial etching was tested as in Example 4 and wasfound to produce good quality copies.

EXAMPLE 8 A polyethylene terephthalate film base was subbed on bothsides with a vinylidene chloride resin as disclosed in Example 4, U.S.Pat. 2,779,864 and then overcoated on one side with a clear gelatinbacking.

A hydrophilic coating, layer 1, was prepared as follows:

Solution I Gelatin200 .g.

Distilled water-4000 ml.

1% aqueous dioctyl sodium sulfosuccinate5 3.5 g.

2% aqueous mucochloric acid-50 ml.

Distilled water97 ml.

The gelatin and water in Solution 1 were digested for minute at 125 F.prior to the addition of the other components.

Solution K, in the amount of 43.5 grams and comprising a mixture of 76%water, 16% silica gel (Si0 of average particle size of 7p), 7% gelatin,and 1% of a mixture of thymol and ethanol (160 g./l.), was then added toSolution I and the resulting mixture coated over the support on the sidewhich was not gelatin backed to a weight of mg./dm. Anorthochromatically sensitized emulsion containing 20 mol percent silverbromide, 80 mol percent silver chloride, 110 gm. of gelatin per mol ofsilver halide, and 0.43 percent of a polymeric dialdehyde hardenerproduced by the oxidation of of the anhydroglucose units of starch, wascoated over layer 1 at a coating weight of 35 mg./dm. (calculated asAgBr).

An oleophilic overcoating, coated over the emulsion at F., was preparedas follows:

Solution L Werner chrome complex of stearic and myrisic acids (40 ml. ofcomplex/8 liters of 40% ethanol) 8 20% aqueous solution of sodiumbisulfite adduct of polyacrolein (av. mol. wt. 400,000) 2.4 10% aqueoussolution of sodium dodecyl sulfate 3.2 Distilled water 112 areas tosoften. The softened areas were rubbed away with a cotton cloth leavinga positive oleophilic image with a hydrophilic background. The preparedprinting plate was mounted on a conventional offset printing press usingone ounce of 14 Baum gum arabic per gallon of water buffered at pH 3.5with H PO and NaH PO as the fountain solution and a quick drying ink.Two thousand good quality copies were obtained.

EXAMPLE 9 A polyethylene terephthalate film base was prepared as inExample 8 except that it was backed on one side with an aqueous gelatinsolution containing C.I. Acid Violet (C.I. refers to Color Index, 2nded., Society of Dyes and Colorists) A gelatin sublayer was prepared andcoated on the side of the base which was not backed. The sublayer wasprepared by mixing gelatin, silica gel of average particle size of 7microns, water, as in Example 8, and

adding 50 ml./200 gm. of gelatin of a 2% aqueous mucochloric acidhardener.

The silver halide emulsion of Example 8 was coated to a weight of 26.5rng./dm. except that it did not contain any polymeric dialdehyde but didcontain 7.0 gm. of the polyacrolein adduct described in Example 8 and 45ml. of 2% aqueous mucochloric acid.

An oleophilic overcoating was prepared by mixing 1.92% of thepolyacrolein adduct described in Example 8, 1% of an ethanol solutioncontaining 37% formaldehyde, 0.34% of a mixture of saturatedmonocarboxylic acids having a C C or C chain length, 1% of a 10% aqueoussolution of cetyl betaine, and water. The oleophilic coating was coatedover the emulsion in a conventional manner.

The photosensitive element was exposed, developed, bleached, and mountedon an offset printing press as in Example 8. Some wear was evident aftershort runs, but such wear was not present if the element were aged forfour days in a tropical oven at F. and 65% relative humidity beforeexposure and processing.

EXAMPLE 10 The following coating solution was prepared:

Solution M Gm. Gelatin 864 10% saponin-ethanol solution 200 Solution K(from Example 8) 182 Water to make 12,000 gm.

The gelatin and 10 liters of water were digested at 125 F. for minutesand allowed to cool to 100 F. prior to the addition of the remainingcomponents. Solution M was then chilled prior to use. Prior to coating,Solution M was heated to 145 F. for 15 minutes and allowed to cool to100 F. at which time 100 ml. of 12.5% aqueous solution of dialdehydestarch as described in Example 8 was added to Solution M. Thepolyethylene terephthalate subbed base of Example 8 was then coated withSolution M.

An orthochromatically sensitized emulsion in an amount of 6,000 gramsand containing 20 mol percent silver bromide, 80 mol percent silverchloride and 110 gm. of gelatin per mole of silver halide was dilutedwith 5,000 ml. of water and melted at 120 F. After cooling to 100 F.,120 ml. of a 10% aqueous sodium dodecyl sulfate solution was added tothe emulsion with 120 ml. of a 12.5% aqueous dialdehyde starch asdescribed in Example 8. This emulsion mixture was coated at 70 ft./min.over the prepared sublayer.

An oleophilic overcoating was then coated over the emulsion. Theovercoating, Solution N, was prepared as follows:

Solution N Werner-type chromium complex of stearic acid1 10 gm. 37%formaldehyde37 ml.

10% aqueous sodium dodecyl sulfate220 ml.

Water to make 12,000 gm.

Solution N was warmed to 85 F. and then coated over the emulsion. Thephotosensitive element was then aged for three days in a tropical ovenas in Example 9. After aging, the element was exposed through the baseto a line and continuous tone copy for 40 seconds at f/ 22, as inExample 8. Exposure was followed by development in a conventionaldeveloper for 75 seconds at 75 F. Development was followed by immersionof the element for seconds in a 2% aqueous acetic acid bath. An etchingsolution was prepared as follows:

Solution 0 Lactic acid, 85%1.5 .0 ml.

Water to make 1000 ml.

The developed element was then etched in Solution 0 at 75 F. for 35seconds. The etched element was placed under running water and thesoftened areas corresponding to the exposed areas were rubbed away tothe hydrophilic subbing layer leaving an oleophilic image on ahydrophilic background.

The printing plate was then rubbed with a commercially availableasphaltum-gum etch as prepared by Western Litho Plate and Supply Co.,St. Louis, Mo. This treatment increased the difference in theoleophilic/hydrophilic properties of the element. After air drying, theprinting plate was mounted on an oifset printing press using conventional ink and a gum arabic-phosphoric acid fountain solution and 500good quality copies produced. There was no unwanted inking or wear ofthe printing plate. Similar results were obtained when Solution Ncontained a complex of myristic acid.

EXAMPLE 11 A polyethylene terephthalate base was subbed as in Example 8and then coated on one side with the following hydrophilic gelatincoating.

Solution P Gelatin-1500 gm.

Thymol (16 gm./ 100 ml. ethanol-l50 gm. 10% saponin-ethanol150 gm.

Water15 l.

Solution P was prepared by heating the water and gelatin to 125 F. for20 minutes, cooling to 100 F., and then adding the remaining components.The coating was then coated at two different weights, mg./dm. and 60mg./dm.

The emulsion of Example 8, without the polymeric dialdehyde hardener wasthen coated over each of the samples at a coating weight of 48 mg./dm.(AgBr equiv.) and at a temperature of 100 F.

A /2% Werner chromium complex of stearic acid (1 gnu/200 ml. of ethanol)wa coated in a 25%/75% ethanol/water solution at 9 f.p.m. and roomtemperature over the emulsion layer. Samples were also coated with a 1%Werner complex of stearic acid.

The samples were then exposed through the base to a halftone image for10 seconds to a General Electric No. 2 Photoflood lamp at a 2ft. maximumdistance. The film was developed as in Example 8, immersed in a 5%acetic acid stop bath for 15 seconds, etched as in Example 8 forseconds, and finally immersed in the stop bath for 15 seconds. Theetching bleached the exposed silver image and softened the adjacentgelatin so that the oleophilic surface coating rubbed away during inkingto provide a fresh hydrophilic surface which would not accept any ink inthe presence of water. When inked with a water, benzene, lithographicink mixture, the oleophilic surface held the ink providing aplanographic printing surface from which many positive copies could beproduced.

EXAMPLE 12 Example 10 was repeated except that the dialdehyde starch inthe sublayer was replaced with 200 ml. of 10% aqueous chrome alum. Thedialdehyde starch in the emulsion was also replaced with chrome alum.The photo- 7 sensitive element was processed as in Example 10 producingsimilar results.

EXAMPLE 13 Solution Q Ml. Werner chromium complex of stearic acid 27.537% formaldehyde 9.25 10% aqueous sodium dodecyl sulfate Water to make3000 ml.

This photosensitive element was exposed and developed as in Example 8except that the element was immersed in the developer for 2 minutes. Thedeveloped element wa short stopped as in Example 8 and etched inSolution 0 for 45 seconds. After etching, the softened exposed areaswere rubbed away as in Example 8 leaving an oleophilic positive image ona hydrophilic background. The paper base printing element was mounted onan offset press as in Example 10 and many good quality copies wereobtained. Similar results were obtained when Solution Q contained acomplex of myristic acid.

When a hydrophilic coating is used between the support and the emulsionlayer, it usually contains silica in average particle size of 312microns and gelatin. However, other adjuvants may be used includingclay, polyacrylic acid, or any adjuvarit containing a hydrophilic group.Various other additives can be incorporated in the coating. Theseinclude hardeners, e.g., chrome alum, formaldehyde, mucochloric acid,dimethylolurea, polymeric dialdehyde starch produced by the oxidation ofof the anhydroglucose units of starch, other polymeric aldehydes,2,5-dimethoxytetrahydrofuran, and other hardeners used in photographicemulsions; gelatin or other suitable binders; and wetting agents such asdioctylsodiurn sulfosuccinate, saponin, etc. It is the purpose of thisovercoating to insure that the difference in the oleophobic/ oleophilicproperties will be sufficiently great such that no ink will adhere tothe oleophobic background causing a spotted background on the printedcopies.

The film supports useful in this invention are not limited topolyethylene terephthalate. If etching is complete to the supportsurface, the support surface must be hydrophilic but if partial etchingor restricted development is used, the support surface need not behydrophilic. These include metals, papers, cellulosic supports and allother bases such as those disclosed in US. Pats. 2,760,863; 2,779,864;3,052,543; and Canadian Pat. 562,672.

The film supports may contain gelatin sublayers as well as resinsublayers as disclosed in Alles, U.S. Pats. 2,779,864 and 2,627,088.Suitable antihalation coatings may be coated over the support. Suchcoatings are disclosed in US. Pats. 1,523,485; 2,085,736; 2,274,782; and2,282,890.

The emulsion layer may be any developable lightsensitive silver saltwhich may be processed by conventional means. These include the silverchloride, silver bromide, emulsions or mixtures thereof. The preferredemulsion contains silver halide grains of bromochloride containing atleast 50 mol percent silver chloride. In addition, direct positiveemulsions containing at least 50 mol percent silver bromide may also besatisfactorily used.

In addition, the emulsion may be either panchromatically sensitized orcontain no optical sensitizer.

The preferred hydrophilic organic colloid binder for the silver halideemulsion is gelatin; however, any natural or synthetic water-permeablehydrophilic colloid binder may be used with the proviso that the binderis susceptible to the bleaching and etching of the acid-peroxide typebleaching solutions. The emulsions may also contain other standardemulsion ingredients such as hardeners, surfactants such as sodiumdodecyl sulfate and sensitizers, etc. as well as other conventionalemulsion additlves.

The water-permeable oleophilic overcoating can be obtained in many ways.One of the oleophilic substances which can be coated onto the outeremulsion surface is a metallo-organic Werner complex, which is acoordina tion complex compound of the type in which a trivalent metal iscoordinated with an organic acid through its carboxylic oxygen atoms.

Trivalent chromium is the most common metal used in forming such complexcompounds. The properties of the Werner-type complexes vary with thecoordinated acid-groups. The long chain acid groups, e.g., stearatogroups, myristo groups, and other hydrophobic groups make the complexesuseful for providing a high degree of oleophilicity. Chromium complexesare generally acidic solutions of the chromium complex in 2-propanol,water, and sometimes acetone. The complex content will vary betweenabout and 35%, depending on the molecular weight of the carboxylic acid.The amount of water varies from about 5% to depending upon the complexin question; the acetone, if any is present, is 'less than 3%; andusually the remainder of the commodity is 2-propanol.

Several methods of preparing the Werner-type chromium complexes usefulin this invention are described in Chromium Complexes, F. B. Hauserman,Advances in Chemistry Series No. 23, American Chemical Society, pp.338-356, (1959). The nomenclature of Werner complexes is also fullydescribed in US. Pats. 2,273,040 and 2,356,161.

Polyacroiein is also suitable as an oleophilic coating. The preferredpolyacrolein is a sodium bisulfite adduct of polyacroleirr having anaverage molecular weight of 400,000. Several methods of polymerizingpolyacrolein are described in Acrolein, C. W. Smith, editor, John Wiley& Sons, Inc., New York, pp. 225233, (1962). Processes for production areavailable in British Pats. 990,263 and 948,669.

The emulsion, subbing layers, and oleophilic overcoating may be coatedin any conventional manner such as those described in US. Pats.3,038,441 and 3,063,868.

The radiation source used for exposing the films of this invention mustfurnish an effective amount of radiation. Such sources include carbonarcs, mercury arcs, electronic flash units, and photographic floodlamps.

When using an element without a hydrophilic support surface, the degreeand time of exposure significantly influences the amount of reducedsilver in the image and the depth of formation of the silver image. Ofcourse, the results obtained with these elements are modified by thetype of developer used but generally, a developer which restrictsdevelopment of the image to the surface of the emulsion is preferredsince then the image develops more rapidly and does not penetrate asdeeply toward the base. A suitable surface developer containsp-methylamino phenol sulfate, sodium hydroxide and sodium sulfite.Restricted surface development will generally require complete etchingand bleaching of the surface image when treated in the acid-peroxidebath.

Other suitable developers include the conventional lithographicdevelopers, e.g., hydroquinone and sodium sulfite, etc. The conventionaldevelopers containing sodium carbonate, potassium bromide, boric acid,etc., may also be satisfactorily used. When development of the image iscomplete with the conventional developers on an element without thehydrophilic support surface, bleaching and etching is restricted to thesurface of the developed image as shown in Examples 4 and 7.

The etch-bleach solutions are generally of the acid peroxide type suchas those disclosed in British Pat. 793,550 published Apr. 16, 1958. Acidpersulfate baths may also be used to etch the film. The etch-bleachprocess includes at least two reactions; (1) oxidation of the developedsilver, (bleaching) and (2) degradation of the gelatin (etching). Therates of these reactions depend on the halide, heavy metal, hydrogenperoxide concentrations, and pH, the latter generally in the range of 1to 3. The most effective pH range was 1.5-1.6. With exposure through thebase followed by development, a negative silver image is obtained. Thedeveloped film is then placed in an etch-bleach bath until the etchingdestroys the developed regions of the emulsion.

The reaction of the light is the opposite when direct positive emulsionsare used causing bleaching and etching to occur in the unexposed areasleaving an oleophilic negative image on a hydrophilic background. Thestronger acid peroxide bleaches referred to above usually bleach andetch the entire image when the silver image is formed near the surfaceas previously described. However, surface bleaching of an image may alsobe effected by shorter bleach times as demonstrated by the previousexamples. When bleaching is not complete, the surface bleached area maybe removed by rubbing, leaving hydrophilic gelatin of the emulsion belowand a positive oleophilic surface image in the background. This gives apartially recessed printing plate having the raised oleophilic surfaceand partially recessed hydrophilic surface.

It has been found that a bleach solution containing ferric ions isexcellent for preparing the partially etched plates of this invention.Such surface bleach contains hydrogen peroxide, a citrate, citric acid,or phosphoric acid, and a salt containing a ferric ion along with ahalide such as chloride, bromide, etc. This surface bleach reacts onlyon the surface to such an extent that the degraded gelatin may beremoved leaving the hydrophilic gelatin of the emulsion as thebackground area for the positive olephilic surface image.

The effects of concentration of the various components in theetch-bleach solutions are described in Centa, J. M., PSA Journal, 11, p.22, (1945); Marriage, A., Brit. Journal of Phot., 91, p. 142, (1944);Luckey, James, and Vanselow, Photo. Sci. Tech., 2, p. 130, (1955).

The product of this invention may be immersed in the developer and theetching solutions but other satisfactory methods of application, such asspraying, rolling, etc., may be used.

Prior to etching, the film element is usually treated in a stop bath,generally acetic acid or equivalent stop baths.

The printing plates of this invention may be mounted on conventionalprinting presses and many good quality copies produced therefrom.

This invention offers a simple process for obtaining lithographicprinting plates. Printing plates of this invention produce tough, highquality copies and have long plate life. The printing plates of thisinvention are also inexpensive to produce since low silver contentemulsions may be used in the process of this invention. The process usedto produce the photographic plates of this invention offers the furtheradvantage of a wide latitude in processing the exposed elements.

When making conventional printing plates, an ordinary negative is madeand this is used for making a positive oleophilic image on the printingplate by contact exposure. The step of producing a negative iseliminated by this invention since the making of the negative isreplaced by the direct preparation of the printing plate as describedabove.

A further advantage of this invention results from the relief imagebeing ink receptive decreasing the possibillty of ink spots in thehydrophilic recessed areas.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A photographic element for the formation of a lithographic printingplate which comprises, in order,

(a) a support having a hydrophilic surface,

(b) an unexposed light-sensitive, hydrophilic waterpermeable organiccolloid silver halide emulsion layer, and

(c) a relatively thin, oleophilic, water-permeable surface coating onthe emulsion layer, said coating consisting of a member selected fromthe group consisting of (1) an oleophilic Werner-type chromium complex,

(2) a polymeric dialdehyde,

(3) mixtures of (1) and (2),

(4) mixtures of (l), (2), or (3) with a compatible binder, and

(5) mixtures of (l), (2), (3), or (4) with a surfactant.

2. A photographic element for the formation of a lithographic printingplate which comprises, in order,

(a) a support having a hydrophilic surface,

(b) an unexposed light-sensitive, hydrophilic waterpermeable organiccolloid silver halide emulsion layer, and

(c) a relatively thin, olephilic, water-permeable surface coating on theemulsion layer, said coating consisting of a member selected from thegroup consisting of (1) an oleophilic Werner-type chromium complex,

(2) polyacrolein,

(3) a polymeric dialdehyde,

(4) mixtures of (1), (2), and (3),

(5) mixtures of (1), (2), (3), or (4) with a surfactant.

3. An element as in claim 1 where said support is a film of polyethyleneterephthalate and said hydrophilic surface contains clay, silicaparticles of 3 to 12 microns in size or polyacrylic acid polymer.

4. An element as in claim 1 where said Werner complex is a complex oftrivalent chromium and myristic acid or stearic acid.

5. An element according to claim 1 wherein said colloid and binder aregelatin.

6. An element as in claim 1 where said coating comprises 30 to 70 partsof said Werner complex, up to 40 parts of formaldehyde and 5 to 40 partsof a surfactant.

7. A process for preparing a lithographic printing plate from aphotosensitive element having a support bearing in order an unexposed,hydrophilic water-permeable organic colloid silver halide emulsion layerand a relatively thin, oleophilic water-permeable surface, said processcomprising:

( 1) exposing said element to an image, by actinic radiation;

(2) developing said exposed element;

(3) treating the developed element in a silver etchbleach solution, and

(4) removing the etched portion of the developed silver image, includingthe oleophilic surface continuous therewith by rubbing to leave arecessed hydrophilic area and an oleophilic image in the unexposedareas.

8. A process according to claim 7 wherein said oleophilic surface is amember selected from the group consisting of (1) an oleophilicWerner-type chromium complex;

(2) polyacrolein;

(3) a polymeric dialdehyde;

(4) mixtures of (l), (2) and (3);

(5) mixtures of (l), (2), (3) or (4) with a compatible binder, and

(6) mixtures of (1), (2), (3), (4) or (5) with a surfactant.

9. A process according to claim 7 wherein said colloid and binding agentare gelatin.

10. A process according to claim 7 wherein the treating with theetch-bleach solution is of a duration to allow only partial removal ofthe gelatin layer in the developed area.

11. A process as in claim 9 Where said etch'bleach solutions are of theacid-peroxide type or acid-persulfate type having apH of 1 to 3.

12. A process as in claim 11 where said etch-bleach solution comprises acopper salt, a water-soluble bromide, hydrogen peroxide and an acid.

13. A process as in claim 9 where the support of said element has ahydrophilic surface and said developed image is removed down to saidhydrophilic support.

14. A process as in claim 10 Where said development is controlled toreduce only the exposed silver halide in the upper portion of the silverhalide emulsion layer.

15. A process as in claim 10 where said developed element is immersed ina dilute acid stop bath solution immediately after development.

16. A process as in claim 10 where said bleach-etch solution containscitric or phosphoric acid, hydrogen peroxide and a ferric salt.

17. A process as in claim 10 where said development is controlled bydeveloping the emulsion surface in a high alkaline p-methylamino phenolsulfate developer of pH 12.0 or greater.

References Cited UNITED STATES PATENTS 4/1922 Schlecht 101-466 6/1964Torstenson 101-466 US. Cl. X.R. 9636.3, 87

